How do they get TV ratings?

Answer 1

The descriptions of the ratings categories serve as the basis for applying ratings.

So, who decides the descriptions of the ratings for broadcast and cable

television networks, or program producers to assign them?

The TV Parental Guidelines Monitoring Board reviews the ratings guidelines and their application to television programming. The Monitoring Board has a Chairman and six members each from the Broadcast Television industry, the cable industry and the program production community. The Chairman of the FCC also selects five non-industry members from public interest groups, for a total of 24 members.

Answer 2

TV ratings are calculated by Nielsen, a company that measures television viewership in the United States. Nielsen uses a representative sample of households equipped with special devices called meters or people-meter to track what they watch. The data collected from these devices is then extrapolated to estimate the total viewership numbers for different shows and time slots.